DESCRIPTION: This study is designed to explore the role of interspecies communication by quorum sensing during probiotic challenge of Streptococcus mutans. The key goal is to determine the role of LuxS and autoinducer type-2 (AI-2)-mediating signaling during interactions of the probiotic bacterium, Lactobacillus reuteri (Reuteri), and the oral pathogen, Streptococcus mutans (Mutans). Laboratory and patient-derived Mutans strains will be tested in the presence of Reuteri for effects on Mutans biofilm formation and Mutans biofilm-associated gene expression. The investigations will emphasize the role of probiotic Reuteri as a possible therapeutic strategy for oral biofilms associated with early childhood caries. By the end of the 2-year study, we Aim to increase our understanding of LuxS-dependent pathways and probiotic Lactobacillus-derwed AI-2 in the control of biofilm formation and colonization by cariogenic Mutans. 1. Explore Lactobacillus reuteri (Reuteri) LuxS-dependent signaling and its effects on Streptococcus mutans (Mutans) LuxS-dependent biofilm formation. 2. Investigate the role of Lactobacillus reuteri (Reuteri) LuxS in regulation of biofilm-related gene expression and biofilm formation by early childhood caries-associated Streptococcus mutans (Mutans). [unreadable] [unreadable]